Various systems have been devised for installation in fireplaces to serve as a means of optimum recovery and utilization of the heat generated and particularly for the purpose of serving as an auxiliary heat source in a space to be heated. For instance it has been proposed in the past to employ a plenum having a series of spaced tubes extending from the plenum with some means of drawing air from the space to be heated through the plenum and over the fireplace grille for heating and recirculation back into the room. Representative of this approach are U.S. Pat. Nos. to Miles 1,681,995; Pierce 1,747,259; Winnett 2,134,935 and Brown 2,642,859. In many cases, such devices are adaptable for pre-existing fireplaces; i.e., can be mounted within the fireplace without substantial reconstruction or modification of the fireplace itself. Others have devised systems which either require positive attachment to the fireplace or modification of the structure of the fireplace itself. For example, U.S. Pat. No. 3,976,047 to Breen et al employs a heat exchanger which includes a radially extending housing having sloped top and bottom walls with air inlet and outlet passages and means for removably mounting the housing above the fireplace hearth such that the rearward end of the air inlet passage is located angularly above the hearth and the apex of the sloped walls defines a flue passage within the rearward wall of the fireplace for expulsion of gases. Other approaches taken have included the use of a forced air circulating system which is usable in combination with a front closure adapted to be placed across the front opening of the fireplace. Representative of this approach is U.S. Pat. No. 4,095,581 to Billmeyer wherein a transparent door seals the open side of the firebox and a housing partially surrounds the firebox to define an air space having a lower inlet and an upper outlet defining the air flow path through the fireplace. The patent to Miles referred to earlier also discloses a circulating system which employs heat resistant doors above the grille and wherein the heated air is circulated through openings in the grille into the room.
While the above and other systems of the type described have met with varying degrees of success, it is highly desirable to provide a fireplace heating system which is conformable for use with fireboxes of varying sizes and not require any positive attachment to the fireplace itself so as to present any difficulties in cleaning or normal use of the fireplace. Further, it is highly desirable that a system of this type be one which is readily usable in open or enclosed fireplaces. For instance, many fireplaces necessitate the use of a front enclosure either as a decorative item or to prevent the entry of smoke into the room. In the past, those systems which have been designed to be self-contained have definite limitations with respect to their utilization in different sized fireplaces and also little in the way of adjustability for example to conform to fireplaces of different depths or heights; or employ a special type of tube structure which must also serve as the log or fuel-supporting portion of the fireplace. Further, those which are adjustable to any extent are not adaptable for use with front enclosures or in most cases require some means of positive attachment to the firebox itself. Representative patents of the type referred to are U.S. Pat. Nos. 4,103,669 to Pauley; 4,112,914 to Brown; and 4,008,704 to Petri.